Process of electrodepositing chromium



' Patented Feb. 9, 1932 UNITED STATES PATENT orrrcs 4 NEW YORK,

PROCESS OF ELECTRODEPOSITING OHRQMIUM Ro Drawing.

This invention relatesto processes of electrodepositing chromium, and aims to provide improvements therein. I

The invention provides a novel process of {5 depositing chromium, by which a good quality of late, both as to structure, brightness, and c or may be obtained, and with good etficiencies for chromium plating. The invention has the further advantage that the l0 electrolytic solution may be used with lead lined tanks without aflecting the lining, chromic acid, especially in combination with acids or salts of stron acids being uite active in attacking most su stances suita 1e for use 1 as containers.

The invention further provides a process of electroplating chromium which may be used without etchlng polished surfaces of artlcles to be plated.

The invention further provides a novel chromium plate, having a lighter orwhlter shade than plate produced by other processes of depositing chromium, this being of importance where the color of silver is to be approximated.

ccording to the present invention, chromic acid is used as the electrolyte. The cata lyst or addition agent is a compoundof fluorine, usually a fluorid, such as chromic or sodium fluorid. We have obtained satisfactory bright plates using as catalyst or addition agents the following:-.

Chromic fluorid Sodium fluorid Fluosilicic acid gLSiE) Fluoboric acid BF,,)

ydrofluoric acid; v a the substances bein "arranged substantially in their order of e ciencies. Hydrofluoric acid, while serviceable, very considerably decreases the efiiciency of plating as com ared with the other substances given above. emperatures from 15 C. to C. are quite suitable, and current densities from to 1 ampere per square inch are suitable, the lower current density being preferred for bright,

e-grained deposit. a The efliciency of the current in de ositing chromium varies with the amount 0 fluorid used in the bath. With a solution containing 250 grams sul hates, gives good results.

' modes of procedure cally described.

compounds Application filed August 12, 1825. Serial No. 49,820.

per liter of chromic acid the best efliciency has been found to be around 3 grams er liter of the fluorine compound, calculate as chromium fluorid, decreasing above and belowthis amount, the fluorine radical being the constituent of importance. In amounts u to about 10 grams per liter of the fluorid the solution does not etch polished surfaces of articles (steel, iron, brass, for example) placed therein for electroplatmg.

Boric acid added to the aforesaid catalyst or addition agents, or even to other catalysts or addition agents such as sulphuric acid and mod e of procedure is as follows :-A bath is made up containing 250 grams per liter of chromic acid (010,) and 3 grams per liter of chromium fluorid (or an equivalent amount of sodium fluorid). The article to be plated, a polished piece of flatwear (a spoon) for example, is connected to the cathode bus-bar and a current of ampere per square inch passed through the solution. A lead-lined tank is used to advantage, as the solution does not attack the lead lining. The starting temperature may be room temperature of 15-20 0., which may increase to about 30 or 35 C. in large tanks, in warm weather, due to the heat of the current. The temperature may be kept constant at a desired temperature by suitable heating and cooling means.

The process may be carried out by other than that herein specifi- The process involving the use of fluorine of the fiuoboric acid type is claimed in our application Serial N 0. 586,700, filed January 14, 1932. 1

What is claimed is:

1. process of electroplating chromium comprising passing an electric current through a solution containing chromic acid and a soluble fluorine-containing compound, said compound being fluosilicic acid, the amount of fiuosilicic acid being that amount which contains the same amount of fluorine as that contained in 10 grams per liter or less of CrF, for a solution containing 250 100 grams per liter CrO and aproportionately higher or lower fiuosilicic acid content for a higher or lower CrO content.

2. A process of electroplating chromium comprising passing an electric current through a solution containing chromic acid and a soluble fluorine containing compound, said compound being fluosilicic acid, the amount of fluosilicic acid being that amount which contains the same amount of fluorine as that contained in approximately three grams per liter of CrF for a solution containing 250 grams per liter Gro and a proportionately higher or lower fiuosilicic acid content for a higher or lower CrO content.

In witness ,whereoi, we have signed our names.

COLIN G. FINK. HUGH DAVID MQLEESE. 

